The bacteria of the oral microbiome form complex multispecies assemblages where species both compete and synergize to colonize each niche in the mouth. In our preliminary research, we discovered a novel aspect of microbial interactions among strains of oral Streptococci via gaseous/volatile compounds produced by some strains. In standard competition experiments these interactions blend with those mediated by diffusible compounds, confuse the picture, often missed, and remain understudied. We show that these interactions are strong and common among Streptococci. Here we will screen a collection of known and novel Streptococci to identify strains interacting via volatile compounds, and determine the nature of these compounds. The novelty of the project is in investigating the nature of previously overlooked or understudied aspects of Streptococcus ecology. This is important because the interactions we will study may influence which strains are able to establish themselves within the oral biofilm, ultimately impacting whether or not the community becomes infectious or remains benign.